The present invention relates to noise reduction. In particular, the present invention relates to removing noise from speech signals received by mobile hand-held devices.
Mobile hand-held devices such as mobile phones and personal digital assistants that provide phone functions or accept speech input are often used in adverse noise environments such as busy streets, restaurants, airports, and cars. The strong ambient noise in these environments can obscure the user's speech and make it difficult to understand what the person is saying.
While noise filtering systems have been developed that attempt to remove noise based on a model of the noise, these systems have not been able to remove all of the noise. In particular, many of these systems have found it difficult to remove noise that consists of other people speaking in the background. One reason for this is that it is extremely difficult, if not impossible, for these systems to determine that a speech signal received by a microphone came from someone other than the person using the mobile device.
For phone headsets, which are kept in position on the user's head by looping the headset over the user's head or ear, systems have been developed that provide more robust noise filtering by relying on additional types of sensors in the headset. In one example, a bone conduction sensor is placed on one end of the head set and is pressed into contact with the skin covering the users skull, ear, or mandible by the resilience of the headset. The bone conduction sensor detects vibrations in the skull, ear or mandible that are created when the user speaks. Using the signal from the bone conduction sensor, this system is able to better identify when the user is speaking and as a result is better able to filter noise in the speech signal.
Although such systems work well for headsets, where contact between the bone conduction sensor and the user is maintained by the mechanical design of the headsets, these systems cannot be used directly in hand-held mobile devices because it is difficult for users to maintain the bone conduction sensor in the proper position and these systems do not take into consideration that the bone conduction sensor may not be held in the proper position.